Electronic component

ABSTRACT

An electronic component includes an electronic component element electrically and mechanically joined to a base member, a plurality of electrode pads of the electronic component element and corresponding electrode lands of the base member being respectively joined together via bumps such that the electronic component element is arranged opposite to the base member. The bumps located along the peripheral portion of the electronic component element have a greater height than that of the bumps located at the central portion of the electronic component element.

This application is a divisional of Ser. No. 09/532,188, filed Mar. 21,2000, now U.S. Pat. No. 6,437,439.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic component in which anelectronic component element, such as a surface acoustic wave element ora semiconductor element, is electrically and mechanically joined to abase member via bump bonding.

2. Description of the Related Art

As electronic components in which electronic component elements aremounted on base members by bump bonding, a surface acoustic wave devicehas been known, for example, which has the structure shown in FIG. 8. Inthis surface acoustic wave device, a surface acoustic wave element 20 iselectrically and mechanically bonded to a base member 10. While apropagation surface of the surface acoustic wave element 20 is opposedto the base member 10, input/output electrode pads 25 a and 25 b and anelectrode pad for grounding 25 c of the surface acoustic wave element 20are respectively joined to corresponding input/output electrode pads 12a and 12 b and an grounding electrode pad 12 c of the base member 10 viabumps 51 a to 51 c which are formed of a material such as Au. Each ofthe bumps 51 a to 51 c is formed to have the same height. Then, a capmember 30 is joined to the base member 10 so as to cover the surfaceacoustic wave element 20, so that the surface acoustic wave element 20is hermetically sealed within a package defined by the base member 10and the cap member 30.

However, in a conventional surface acoustic wave device, when amechanical stress such as an impact caused by dropping the device or athermal stress such as variation in ambient temperature is appliedthereto, mechanical damages such as fracture and exfoliation areproduced in bumps 51 a and 51 b and electrode pads 25 a and 25 b whichare respectively bump-bonded thereto. Such mechanical damage usuallyoccurs in a peripheral portion of the base member 10 and the surfaceacoustic wave element 20, and the failure in the bump bonding processcauses the electronic device to have faulty characteristics. This isbecause the damage caused by the mechanical stress or the thermal stressis often concentrated on bumps located along a peripheral portioninstead of bumps located at the central portion.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide an electronic component wave devicewhich achieves a high degree of reliability and prevents problems andfaulty connections conventionally occurring during bump bonding byrelieving the stress applied to the bumps located along a peripheralportion of a base member and an electronic component element.

According to a preferred embodiment of the present invention, anelectronic component includes a base member having a plurality ofelectrode lands, an electronic component element having a plurality ofelectrode pads and being electrically and mechanically joined to thebase member, a plurality of bumps located between the electroniccomponent element and the base member, the plurality of electrode padsof the electronic component element and the corresponding electrodelands of the base member being respectively joined together via thebumps such that the electronic component is opposite to the base member,wherein the bumps located at the peripheral portion of the electroniccomponent element have a greater height than that of the bumps locatedin the central portion of the electronic component element.

As a result of this unique structure, the stress applied to the bumpslocated at the peripheral portion is relieved because the bumps locatedat the peripheral portion, in which the stress is prone to concentrate,have a greater height than that of the bumps located in the centralportion. Consequently, bonding problems such as damage to electrodes orbump bonding portions and exfoliation are reliably prevented, resultingin improved reliability of the electronic component.

In order to obtain bumps having a greater height at the peripheralportion than that of the bumps located at the central portion, variousmethods such as changing the film thickness of electrode lands formed onthe base member; forming the base member to have a convex shape; formingthe base member to have a curved shape; or changing the film thicknessof electrode pads of the surface acoustic wave element, may be used.Also, any combination of these methods may also be used.

In the above-mentioned configuration, it is preferable that thedifferences between heights of the bumps are about 1 μm to about 10 μm.

In addition, preferred embodiments of the present invention provide anelectronic component in which a surface acoustic wave element or asemiconductive element, or other suitable electronic component element,is electrically and mechanically joined to a base member via bumpbonding.

According to preferred embodiments of the present invention, the bumpslocated at the peripheral portion, in which the stress is prone toconcentrate, have a greater height than that of the bumps located at thecentral portion so as to relieve the stress applied to the bumps locatedat the peripheral portion, so that bonding problems such as damage toelectrodes located at bumps or bump bonding portions and exfoliation arereliably prevented.

For the purpose of illustrating the invention, there is shown in thedrawings several forms which are presently preferred, it beingunderstood, however, that the invention is not limited to the precisearrangements and instrumentalities shown.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a surface acoustic wave device accordingto a first preferred embodiment of the present invention.

FIG. 2 is a plan view of a surface acoustic wave element according tothe first preferred embodiment of the present invention.

FIG. 3 is a sectional view of a surface acoustic wave device accordingto a second preferred embodiment of the present invention.

FIG. 4 is a sectional view of a surface acoustic wave device accordingto a third preferred embodiment of the present invention.

FIG. 5 is a sectional view of a surface acoustic wave device accordingto a fourth preferred embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the height of bumpsand stress caused by thermal stress.

FIG. 7 is a graph showing the relationship between a difference in bumpheights and the failure rate due to stress.

FIG. 8 is a sectional view of a conventional surface acoustic wavedevice.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention areexplained in detail with reference to the drawings.

An electronic component according to one preferred embodiment of thepresent invention will be described below in the context of a surfaceacoustic wave device. However, other electronic component elements mayalso be included in other types of electronic components of the presentinvention.

A structure of a surface acoustic wave device according to a firstpreferred embodiment of the present invention is shown in FIGS. 1 and 2.FIG. 1 is a sectional view of the surface acoustic wave device whileFIG. 2 is a plan view of a surface acoustic wave element.

In the surface acoustic wave device according to the present preferredembodiment, a plurality of electrode pads 25 a to 25 c of a surfaceacoustic wave element 20 and a plurality of electrode lands 12 a to 12 con the top surface within a recessed area of a base member 10 arerespectively bump-bonded together via bumps 51 a to 51 c and a capmember 30 is joined to the base member 10 so as to cover the surfaceacoustic wave element 20, so that the surface acoustic wave element 20is hermetically sealed within a package (within a space) defined by thebase member 10 and the cap member 30.

The base member 10 preferably has a recessed shape and is preferablyformed by stacking a plurality of layers of ceramic material or othersuitable material. On the top surface of the recessed area, which is amounting surface of the surface acoustic wave element, an electrodepattern including electrode lands for input-output 12 a and 12 b and anelectrode land for grounding 12 c is provided. On the bottom surface ofthe base member 10, terminal electrodes for input-output 14 a and 14 band a terminal electrode for grounding 14 c are provided. The electrodelands 12 a to 12 c are preferably made of thick film electrodes of W orMo, or other suitable material, with Ni or Au preferably being platedthereon. The electrode lands 12 a, 12 b, and 12 c are respectivelyconnected to terminal electrodes 14 a, 14 b, and 14 c via through-holeelectrodes or edge electrodes (not shown). This surface acoustic wavedevice is mounted on a mounting substrate (circuit board) using thebottom surface of the base member 10 as a mounting surface.

The surface acoustic wave element 20 preferably includes a piezoelectricsubstrate 21, for example, as shown in FIG. 2. On the top surface of thepiezoelectric substrate 21, an electrode pattern including IDTelectrodes 22, reflector electrodes 23, and electrode pads 25 a to 25 cconnected to each of the IDT electrodes 22, are provided. The electrodepattern is preferably made of Al or an alloy including Al and formed bya known thin film forming method. In addition, in FIG. 2, portionsindicated by circles with broken lines indicate locations of bumpbonding portions. The piezoelectric substrate 21 is preferably made of apiezoelectric material such as lithium tantalate, lithium niobate, andcrystal or other suitable material.

The surface acoustic wave element 20 is electrically and mechanicallyjoined to a base member 10 in a face-down configuration, that is, thepropagation surface of the surface acoustic wave device on which the IDTelectrodes 22, and other elements, are provided is opposed to theelement-mounting surface of the base member 10. The electrode pads 25 a,25 b, and 25 c are respectively joined to corresponding electrode pads12 of the base member 10 via respective bumps 51 a, 51 b, and 51 c. Thisbonding is performed by applying heat or simultaneously applying heatand ultrasonic waves to fuse bumps 51 a to 51 c. The bumps 51 to 51 care preferably made of Au or a metal including Au as the principalingredient. The bumps 51 to 51 c are preferably provided on theelectrode pads 25 a to 25 c of the surface acoustic wave element 20 inadvance by a ball bonding method. In addition, solder may be used toform the bump, which may be formed on the electrode land of the basemember by a method such as printing.

An appropriate metallic material such as an alloy including Fe—Ni ispreferably used to form the cap member 30, which may be plated thereonas desired. The cap member 30 is joined to the base member 10 so as tocover the surface acoustic wave element 20, via a soldering materialsuch as solder having a high melting point, an alloy of Au—Sn, or glasshaving a low melting point or other suitable material.

In the surface acoustic wave device according to the present preferredembodiment, the film of the electrode land for grounding 12 c located atan approximately central portion of the base member 10 has a greaterthickness than that of the electrode lands for input-output 12 a and 12b located along the peripheral portion. That is, the top surface of theelectrode land for grounding 12 c is higher than the electrode lands forinput-output 12 a and 12 b. Thereby, the bumps 51 a and 51 b located atthe peripheral portion of the surface acoustic wave element 20 have agreater height “h1” than a height “h2” of the bumps 51 c located at thecentral portion of the surface acoustic wave element 20. In order toincrease the film thickness of the electrode land for grounding 12 c,the electrode film preferably made of W or Mo, or Ni or Au plating has athickness that is greater than that of the electrode lands forinput-output 12 a and 12 b.

It is to be noted that the bumps “in the central portion” and the bumps“in the peripheral portion” are referred to in terms of the distancesfrom the approximate center of the surface acoustic wave element 20.More specifically, as shown in FIG. 2, the distance between the circleson the electrode pads 25 c which indicate the position of the bumps 51 cand the approximate center “C” of the surface acoustic wave element 20are smaller than the distance between the circles on the electrode pads25 a and 25 b which indicate the position of the bumps 51 a and 51 b andthe center “C”. That is, the bumps 51 a and 51 b are located father thanthe bumps 51 c from the approximate center of the surface acoustic waveelement.

Because of this unique structure and arrangement, when mechanical orthermal stress is applied, the stress applied to the bumps 51 a and 51 blocated along the peripheral portion, in which the stress is apt toconcentrate, is relieved, so that mechanical damage such as fracture andexfoliation are prevented from occurring in the bumps and the electrodepads bump-bonded thereto. Therefore, with this preferred embodiment,faulty joining such as breaking of wire in the bump and faulty bumpbonding are reliably prevented, resulting in greatly improvedreliability of the electronic component.

A surface acoustic wave device according to a second preferredembodiment will be described with reference to FIG. 3. In this preferredembodiment, a convex portion 16 is preferably formed in the base member10 so that a portion for forming the electrode land for grounding 12 c,that is the approximate central portion of the element mounting surface,projects toward the surface acoustic wave element 20. Each of electrodelands 12 a to 12 c preferably have substantially the same filmthickness. The other structure is similar to that of the first preferredembodiment. That is, in the second preferred embodiment, a portion ofthe base member 10 has a greater thickness so that the top surface ofthe electrode land for grounding 12 c is higher than the electrode landsfor input-output 12 a and 12 b. As a result, the bumps 51 a and 51 blocated along the peripheral portion of the surface acoustic waveelement 20 have a greater height than that of the bumps 51 c at theapproximate central portion. As a result of this unique structure, thesame advantages achieved by the first preferred embodiment are achievedin the second preferred embodiment.

A surface acoustic wave device according to a third preferred embodimentwill be described with reference to FIG. 4. In this preferredembodiment, the base member 10 is curved so that a forming portion ofthe electrode land for grounding 12 c, that is the central portion ofthe element mounting surface, is close to the surface acoustic waveelement 20. Each of electrode lands 12 a to 12 c preferably has the samefilm thickness. The other structure of this preferred embodiment issimilar to that of the first preferred embodiment. That is, in the thirdpreferred embodiment, the section of the base member 10 preferably has aroughly circularly curved surface so as to increase the height of thecentral portion of the element mounting surface, so that the top surfaceof the electrode land for grounding 12 c higher than the electrode landsfor input-output 12 a and 12 b. Thereby, the bumps 51 a and 51 b locatedalong the peripheral portion of the surface acoustic wave element 20have a greater height than that of the bumps 51 c at the centralportion.

Because of this unique structure and arrangement, the advantagesachieved by the preferred embodiments described above are also achievedin the third preferred embodiment. The structure of the third preferredembodiment is simple in comparison to the structure of the first andsecond preferred embodiments, resulting in easy manufacturing.

A surface acoustic wave device according to a fourth preferredembodiment will be described with reference to FIG. 5. In this fourthpreferred embodiment, the films of the electrode pads for grounding 25 clocated at the approximate central portion of the surface acoustic waveelement have a larger thickness than that of the electrode pads forinput-output 25 a and 25 b located along the peripheral portion of thesurface acoustic wave element. The electrode lands 12 a to 12 c of thebase member 10 preferably have the same film thicknesses. The otherstructure of the fourth preferred embodiment is preferably similar tothat of the first preferred embodiment. That is, in the fourth preferredembodiment, the bottom surfaces of the electrode pads for grounding 25 care lower than those of the electrode pads for input-output 25 a and 25b. Thereby, the bumps 51 a and 51 b located along the peripheral portionof the surface acoustic wave element 20 have a larger height than thatof the bumps 51 c at the approximate central portion. Because of thisunique structure and arrangement, the advantages achieved by thepreferred embodiments described above are also achieved in the fourthpreferred embodiment.

In addition, each of structures described in the above-mentionedpreferred embodiments may be combined to form bumps located along theperipheral portion to have a greater height than that of bumps at thecentral portion.

FIG. 6 is a graph showing the relationship between the height of thebump and the stress imparted by thermal stress. In the example shown inFIG. 6, the stresses applied to the bumps are relatively shown when theheight of the bump was changed, wherein the base member was formed ofalumina, the bump had a diameter of about 120 μm, and two distancesbetween the approximate center of the surface acoustic wave element andthe bump of about 300 μm and about 600 μm were evaluated. In addition,as for the stress due to thermal stress, there is a stress produced whenthe temperature of joining such as bump bonding or joining of the basemember to the case member is reduced to room temperature.

As shown in FIG. 6, the stress applied to the bump decreases withincreasing height of the bump, and increases with increasing distancebetween the approximate center of the surface acoustic wave element andthe bump. That is, the stress increases with increasing spacing betweenthe bump forming position and the approximate center of the surfaceacoustic wave element. Therefore, when the height of bumps is the same,the stress applied to the bumps located along the peripheral portion isrelatively larger than that of the bumps located at the approximatecentral portion.

Accordingly, in preferred embodiments of the present invention, thestress applied to the bumps located along the peripheral portion isgreatly reduced such that the bumps located along the peripheral portionhave a greater height than the bumps located in the approximate centralportion. The reason is that the stress tends to be absorbed into thebump itself with increasing height of the bump.

That is, in each of preferred embodiments described above, the filmthickness of the electrode land, the thickness of the convex portion, orthe degree of the curvature in the base member or the film thickness ofthe electrode pad in the surface acoustic wave element is establishedsuch that each bump has a greater height in accordance with increasingdistance from the approximate center of the surface acoustic waveelement.

Next, the difference in height of bumps will be considered. FIG. 7 is agraph showing the relationship between the difference in height betweenthe bumps located along the peripheral portion and the bumps located inthe approximate central portion and a failure rate due to the mechanicaland the thermal stress. More particularly, in FIG. 7, the solid lineindicates the failure by exfoliation of the electrode pads forinput-output 25 a and 25 b shown in the respective drawings for thepreferred embodiments due to the mechanical and the thermal stress whilethe broken line indicates the failure caused by insufficient bondingbetween the electrode lands for input-output 12 a and 12 b and the bumps51 a and 51 b.

As shown in FIG. 7, when differences in height between the bumps locatedalong the peripheral portion and the bumps located at the approximatecentral portion are substantially equal to or higher than about 1 μm,the failure due to the mechanical and the thermal stress is prevented.However, when differences in height between bumps are not less thanabout 10 μm, the bonding between bumps and electrode lands isdeteriorated during assembling of the surface acoustic wave device, sothat the failure caused by bonding problems such as insufficient bondingbetween the electrode land and the bump occur. Therefore, it ispreferable that differences in height between the bumps range from about1 μm to about 10 μm, while the bumps located along the peripheralportion have a larger height than the bumps located at the approximatecentral portion.

In addition, the electrode pattern is not limited to the one shown inFIG. 2. The surface acoustic wave element may have electrode patternsdefined by one or no less than three IDTs. That is, the number andlocations of electrode pads of the surface acoustic wave element and thenumber and locations of electrode lands of the base member are notlimited to those in the above-mentioned preferred embodiments. Electrodepads and electrode lands for input-output may be located toward theapproximate central portion, while electrode pads and electrode landsfor grounding may be located along the peripheral portion.

The shapes of the base member and the cap member are not limited tothose in the above-mentioned preferred embodiments. The package may beformed of a plate shaped base member and a recessed shaped cap member.

The above-mentioned preferred embodiments have been described in thecontext of the surface acoustic wave device. However, the presentinvention may be a applied to a semiconductor device in which asemiconductor element is bump-bonded to a base member or to otherelectronic components.

While preferred embodiments of the invention have been disclosed,various modes of carrying out the principles disclosed herein arecontemplated as being within the scope of the following claims.Therefore, it is understood that the scope of the invention is not to belimited except as otherwise set forth in the claims.

What is claimed is:
 1. An electronic component comprising: a base memberhaving a plurality of electrode lands; an electronic component elementhaving a substrate and a plurality of electrode pads provided on thesubstrate, the electronic component element being electrically andmechanically joined to the base member; a plurality of bumps locatedbetween the electronic component element and the base member, theplurality of electrode pads of the electronic component element and thecorresponding electrode lands of the base member being respectivelyjoined together via the bumps such that the electronic component isopposite to the base member and the plurality of bumps are in directcontact with the electrode pads of the electronic component element andthe corresponding electrode lands of the base member; wherein the bumpslocated at the peripheral portion of the electronic component elementhave a height that is greater than the height of the bumps located inthe approximate central portion of the electronic component element byabout 1 μm to about 10 μm; and the base member is curved so that aforming portion of the electrode land located at the approximate centralportion is close to the electronic component element.
 2. A method ofmanufacturing an electronic component, comprising the steps of:providing a base member having a plurality of electrode lands; providingan electronic component element having a substrate and a plurality ofelectrode pads provided on the substrate, the electronic componentelement being electrically and mechanically joined to the base member;forming a plurality of bumps on one of the base member and theelectronic component element; arranging the electronic component elementopposite to the base member; and joining the base member and theelectronic component element via the plurality of bumps between theelectronic component element and the base member, the plurality ofelectrode pads of the electronic component element and the correspondingelectrode lands of the base member being respectively joined togethervia the bumps such that the electronic component element is opposite tothe base member and the plurality of bumps are in direct contact withthe electrode pads of the electronic component element and thecorresponding electrode lands of the base member; wherein the step offorming the bumps includes forming the bumps located at the peripheralportion of the electronic component element to have a height that isgreater than the height of the bumps located in the approximate centralportion of the electronic component element by about 1 μm to about 10μm; and the base member is curved so that a forming portion of theelectrode lands located at the approximate central portion is close tothe electronic component element.